Nonisothermal kinetics study with advanced isoconversional procedure and DAEM

The precursor of LiNiPO₄ was synthesized by solid-state reaction at low-heating temperature using LiOH·H₂O and NH₄NiPO₄·H₂O as raw materials. LiNiPO₄ was obtained by calcining the precursor. Based on the advanced isoconversional procedure and the distributed activation energy model (DAEM), the activation energies calculated indicated that the thermal process involved two stages which stage II was a kinetically complex process, but stage I was single-step process. The most probable mechanism for the stage I is random nucleation and subsequent growth. DAEM and nonlinear model-fitting method were applied to study the stage II of decomposition process of the precursor. The distributions of activation energy, f(E _a) and values of preexponential factor A of the stage II of the thermal decomposition of precursor were obtained on the basis of DAEM. The results of nonlinear model-fitting method showed the most probable mechanisms of the parallel reactions for stage II are chemical reaction and nucleation.     

Preparation and thermal properties of poly[acrylonitrile-co-(β-methylhydrogen itaconate)] used as carbon fiber precursor

In order to replace terpolymer with bipolymer, a bifunctional comonomer β-methylhydrogen itaconate (MHI) containing carboxyl group and ester group was synthesized to prepare poly[acrylonitrile-co-(β-methylhydrogen itaconate)] [P(AN-co-MHI)] bipolymers used as carbon fiber precursor for improving the stabilization and spinnability at the same time. The P(AN-co-MHI) bipolymers with different monomer feed ratios were characterized by elemental analysis, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The results show that both the polymerization conversion and molecular mass of P(AN-co-MHI) reduce with the increasing MHI amounts in the feed due to the larger molecular volume of MHI than acrylonitrile (AN). The monomer reactivity ratios were calculated by Fineman–Ross and Kelen–Tüdõs methods, the results show good agreement and MHI possesses higher reactivity than AN. Two parameters $ E_{\text{s}} = A_{{1,629\,{\text{cm}}^{ - 1} }} /A_{{2,244\,{\text{cm}}^{ - 1} }} $ and $ SI = (I_{0} - I_{\text{S}} )/I_{0} $ were defined to evaluate the extent of stabilization, and the activation energy (E _a) of the cyclization was calculated by Kissinger method and Ozawa method. The FTIR, XRD, and DSC results show that P(AN-co-MHI) bipolymers exhibit significantly improved stabilization characteristics than PAN homopolymer, such as larger extent of stabilization, lower initiation temperature, and smaller E _a of cyclization, which is attributed to the ionic initiation by MHI comonomer and it is beneficial to preparing high-performance carbon fiber.     

Pyrolysis and combustion model of oil sands from non-isothermal thermogravimetric analysis data

Thermogravimetric (TG) data of oil sand obtained at Engineering Research Center of Oil Shale Comprehensive Utilization were studied to evaluate the kinetic parameters for Indonesian oil sand samples. Experiments were carried out at heating rates of 5, 15, and 25 °C min^?1 in nitrogen, 10, 20, and 50 °C min^?1 in oxygen atmosphere, respectively. The extent of char combustion was found out by relating TG data for pyrolysis and combustion with the ultimate analysis. Due to distinct behavior of oil shale during pyrolysis, TG curves were divided into three separate events: moisture release, devolatilization, and evolution of fixed carbon/char, where for each event, kinetic parameters, based on Arrhenius theory, were calculated. Coats–Redfern method, Flynn–Wall–Ozawa method, and distributed activation energy model method have been used to determine the activation energies of degradation. The methods are compared with regard to their characteristics and the ease of interpretation of the thermal kinetics. Activation energies of the samples were determined by three different methods and the results are discussed.     

Improvement of electrochemical performance for Li-rich spherical Li1.3[Ni0.35Mn0.65]O2+x modified by Al2O3

The Li-rich Li_1.3[Ni_0.35Mn_0.65]O_2+x microspheres are firstly prepared and subsequently transferred into the Al₂O₃-coated Li-rich Li_1.3[Ni_0.35Mn_0.65]O_2+x microspheres by a simple deposition method. The as-prepared samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and charge/discharge tests. The results reveal that the Al₂O₃-coated Li-rich Li_1.3[Ni_0.35Mn_0.65]O_2+x sample has a typical α-NaFeO₂ layered structure with the existence of Li₂MnO₃-type integrated component, and the Al₂O₃ layer is uniformly coated on the surface of the spherical Li-rich Li_1.3[Ni_0.35Mn_0.65]O_2+x particles with a thickness of about 4 nm. Importantly, the Al₂O₃-coated Li-rich sample exhibits obviously improved electrochemical performance compared with the pristine one, especially the 2 wt.% Al₂O₃-coated sample shows the best electrochemical properties, which delivers an initial discharge capacity of 228 mAh g^?1 at a rate of 0.1 C in the voltage of 2.0–4.6 V, and the first coulombic efficiency is up to 90 %. Furthermore, the 2 wt.% Al₂O₃-coated sample represents excellent cycling stability with capacity retention of 90.9 % at 0.33 C after 100 cycles, much higher than that of the pristine one (62.2 %). Particularly, herein, the typical inferior rate capability of Li-rich layered cathode is apparently improved, and the 2 wt.% Al₂O₃-coated sample also shows a high rate capability, which can deliver a capacity of 101 mAh g^?1 even at 10 C. Besides, the thin Al₂O₃ layer can reduce the charge transfer resistance and stabilize the surface structure of active material during cycling, which is responsible for the improvement of electrochemical performance of the Li-rich Li_1.3[Ni_0.35Mn_0.65]O_2+x .     

Nickel‐Catalyzed Site‐Selective Amidation of Unactivated C(sp3)H Bonds

Intramolecular dehydrogenative cyclization of aliphatic amides was achieved on unactivated sp³ carbon atoms by a nickel‐catalyzed C?H bond functionalization process with the assistance of a bidentate directing group. The reaction favors the C?H bonds of β‐methyl groups over the γ‐methyl or β‐methylene groups. Additionally, a predominant preference for the β‐methyl C?H bonds over the aromatic sp² C?H bonds was observed. Moreover, this process also allows for the effective functionalization of benzylic secondary sp³ C?H bonds.     

Study on the interaction between urea and cellulose by combining solid-state 13C CP/MAS NMR and extended Hückel charges

In this article, solid-state ¹³C CP/MAS NMR combined with extended Hückel charges was applied to investigate the interaction between urea and cellulose in the NaOH/urea aqueous solvent system. Direct experimental evidence was provided to support the interaction between urea and cellulose. The solid-state ¹³C CP/MAS NMR results revealed that complicated complexes are formed by urea, NaOH and cellulose in the solution. Excess urea exists in a free state, which explains why 7 wt% NaOH/12 wt% urea/81 wt% H₂O is the optimal ratio selection to dissolve cellulose. Based on the correlation in which the computed extended Hückel charge on carbon of urea is approximately inversely proportional to its ¹³C chemical shift, a possible interaction model of cellulose, NaOH and urea was proposed. Interactions exist between any two of urea, NaOH and cellulose, which results in the cellulose chain being surrounded by NaOH and urea molecules. NaOH and urea may be in the same surface layer of cellulose chains.     

Oxidative Cross‐Coupling of Allenyl Ketones and Organoboronic Acids: Expeditious Synthesis of Highly Substituted Furans

Allenyl ketones are employed as coupling partners in palladium‐catalyzed oxidative cross‐coupling reactions with organoboronic acids. This reaction constitutes an efficient methodology for the synthesis of highly substituted furan derivatives. Palladium‐carbene migratory insertion is proposed as the key step in this transformation.     

Mass Transfer Analysis of Growth and Substance Metabolism of NSCs Cultured in Collagen-Based Scaffold In Vitro

The aim of this study is to analyze the growth and substance metabolism of neural stem cells (NSCs) cultured in biological collagen-based scaffolds. Mass transfer and metabolism model of glucose, lactic acid, and dissolved oxygen (DO) were established and solved on MATLAB platform to obtain the concentration distributions of DO, glucose, and lactic acid in culture system, respectively. Calculation results showed that the DO influenced their normal growth and metabolism of NSCs mostly in the in vitro culture within collagen-based scaffolds. This study also confirmed that 2-mm thickness of collagen scaffold was capable of in vitro cultivation and growth of NSCs with an inoculating density of 1?×?10⁶ cells/mL.     

DNA Nanoribbon-Templated Self-Assembly of Ultrasmall Fluorescent Copper Nanoclusters with Enhanced Luminescence

Fluorescent copper nanoclusters (CuNCs) have been widely used in chemical sensors, biological imaging, and light-emitting devices. However, individual fluorescent CuNCs have limitations in their capabilities arising from poor photostability and weak emission intensities. As one kind of aggregation-induced emission luminogen (AIEgen), the formation of aggregates with high compactness and good order can efficiently improve the emission intensity, stability, and tunability of CuNCs. Here, DNA nanoribbons, containing multiple specific binding sites, serve as a template for in situ synthesis and assembly of ultrasmall CuNCs (0.6 nm). These CuNC self-assemblies exhibit enhanced luminescence and excellent fluorescence stability because of tight and ordered arrangement through DNA nanoribbons templating. Furthermore, the stable and bright CuNC assemblies are demonstrated in the high-sensitivity detection and intracellular fluorescence imaging of biothiols.     

Light-Driven Crawling of Molecular Crystals by Phase-Dependent Transient Elastic Lattice Deformation

The light-driven crawling of a molecular crystal that can form three phases, (α, β, and γ) is presented. Laser irradiation of the molecular crystal can generate phase-dependent transient elastic lattice deformation. The resulting elastic lattice deformation that follows scanning irradiation of a laser can actuate the different phases of molecular crystal to move with different velocity and direction. Because the γ phase has a large Young's modulus (ca. 26 GPa), a force of 0.1 μN can be generated under one laser spot. The generated force is sufficient to actuate the γ-formed molecular crystals in a wide dimensional range to move longitudinally at a velocity of about 60 μm min⁻¹, which is two orders of magnitude faster than the α and β phases.